The present invention relates generally to a voltage step-up circuit, and particularly, to a voltage step-up circuit of a type including a pair of diode-connected MOS field effect transistors serially connected between a power supply terminal and an output terminal of the circuit in a forward direction for conduction from the power supply terminal to the output terminal and a capacitor connected to a serial interconnection between the transistors, so that a charge pump action depending on an externally input periodical signal permits a higher voltage than a power supply voltage to be output.